1. Field of the Invention
The present invention relates to an information recording method and an information recording apparatus for recording digital data in high density by forming pits on a recording medium such as an optical disk or the like.
2. Description of the Related Art
In general, digital data (digital signal) is recorded as pits on a recording medium such as an optical disk or the like. According to a conventional optical disk such as a CD or the like, there has been employed a method for recording digital data on the optical disk by changing the length of pits or the distance between pits based on the digital data.
In order to increase the recording density of digital data, there has recently been proposed a recording method different from the above-described recording method. This recording method is called a Single Carrier Independent Pit Edge Recording (SCIPER) system.
FIG. 1 shows a relationship between pits and digital data according to the SCIPER system. As shown in FIG. 1, in the SCIPER system, pits PT are disposed on a track of an optical disk with a predetermined period T between the pits, regardless of the contents of digital data. The contents of the digital data are represented at each position of edges E1 and E2 of each pit PT. In other words, for each pit PT, the front edge E1 positioned at the front side of a peripheral direction of the optical disk is determined by the contents of a certain digital data. The rear edge E2 positioned at the rear side of the peripheral direction of the optical disk is determined based on the contents of another digital data. As explained above, according to the SCIPER system, the recording of the digital data is achieved by stepwise shifting the positions of the edges E1 and E2 of each PT based on the digital data.
In the case of using a digital data having three values of xe2x80x9cxe2x88x921xe2x80x9d, xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d, for example, the position of the front edge E1 of a pit PT shifts stepwise in three stages as shown in FIG. 1. For example, when the digital data is xe2x80x9c1xe2x80x9d, the position of the front edge E1 is P1. When the digital data is xe2x80x9c0xe2x80x9d, the position of the front edge E1 is P2. When the digital data is xe2x80x9cxe2x88x921xe2x80x9d, the position of the front edge E1 is P3.
The position of the rear edge E2 of the pit PT also shifts stepwise in three stages in a similar manner. For example, when the digital data is xe2x80x9cxe2x88x921xe2x80x9d, the position of the rear edge E2 is P4. When the digital data is xe2x80x9c0xe2x80x9d, the position of the rear edge E2 is P5, and when the digital data is xe2x80x9c1xe2x80x9d, the position of the rear edge E2 is P6.
In the case of reproducing the digital data recorded by the SCIPER system, shown in FIG. 1, a light spot SP is formed by irradiating a laser beam onto the optical disk, and the pit PT is traced with this light spot SP. A reflection beam of this light spot is converted into a detection signal. In this detection signal, differences of the position of each of the edge E1 and edge E2 are represented as changes in the level. Accordingly, by comparing the changes of the level of this detection signal with a predetermined reference level, it is possible to decide the contents of the digital data, that is, xe2x80x9cxe2x88x921xe2x80x9d, xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d.
However, at the time of reproducing the recording data recorded by the SCIPER system, components due to inter-symbol interference are superimposed in the detection signal. Therefore, it is not easy to accurately decide the contents of the digital data.
Further, when the signal to noise ratio (S/N ratio) of a reproducing apparatus is low, what is called system noise is superimposed in the detection signal, in addition to the components due to the inter-symbol interference. This makes it further difficult to make an accurate decision of the contents of the digital data.
If what is called media noise of the optical disk is further superimposed in the detection signal in addition to the above, it becomes much more difficult to make an accurate decision of the contents of the digital data.
It is therefore an object of the present invention to provide an information recording method and an information recording apparatus capable of achieving an accurate reproduction of data recorded by the SCIPER system, by eliminating the inter-symbol interference.
The above-stated object can be achieved by the method in accordance with the present invention. This method is an information recording method of recording a digital signal representing digital data onto a recording medium by changing a position of each edge of each of a plurality of pits in accordance with the digital signal. The method is used in a recording and reproducing system comprising a recording apparatus for recording the digital signal onto the recording medium by changing the position of each edge of each of the plurality of pits in accordance with the digital signal, and a reproducing apparatus for reproducing the digital signal recorded on the recording medium. The method has the processes of: receiving the digital signal to be recorded; generating a predicted inter-symbol interference signal by predicting inter-symbol interference contained in a reproduced signal from the recording medium when a reproducing process is carried out with respect to the recording medium by the reproducing apparatus, on the basis of predetermined characteristics of a recording process in the recording apparatus, predetermined characteristics of the reproducing process, and the received digital signal; generating a compensated digital signal by subtracting the predicted inter-symbol interference signal from the received digital signal; and recording the compensated digital signal onto the recording medium by continuously changing the position of each edge of each of the plurality of pits in proportion to the compensated digital signal.
The digital signal representing the digital data is recorded onto the recording medium by the recording apparatus. This digital signal is then reproduced from the recording medium. At this time, this reproduced signal contains inter-symbol interference. This inter-symbol interference is produced by influence of characteristics of the recording process of the recording apparatus, characteristics of the reproducing process of the reproducing apparatus, and the digital signal. Therefore, the inter-symbol interference can be predicted on the basis of the characteristics of the recording process of the recording apparatus, characteristics of the reproducing process of the reproducing apparatus and the digital signal, and a replica of the inter-symbol interference can be created as a signal. If this replica signal is subtracted from the digital signal before the digital signal is actually recorded onto the recording medium, it is possible to cancel the inter-symbol interference in the reproduced signal at the time of reproduction.
In the method according to the present invention, a predicted inter-symbol interference signal is firstly generated on the basis of predetermined characteristics of the recording process in the recording apparatus, predetermined characteristics of the reproducing process in the reproducing apparatus and the received digital signal. A compensated digital signal is next generated by subtracting the predicted inter-symbol interference signal from the received digital signal. This compensated digital signal is then recorded onto the recording medium.
To record the compensated digital signal, a plurality of pits corresponding to the compensated digital signal are formed on the recording medium. As a result of this, the position of each edge of each pit is continuously changed in proportion to the compensated digital signal. As stated above, the compensated digital signal is generated by subtracting the predicted inter-symbol interference signal from the digital signal. Since the level of the inter-symbol interference signal is continuously changed with a continuous change of the amount of the inter-symbol interference contained in the reproduced signal, the compensated digital signal is also continuously changed. Therefore, the position of each edge of each pit is also continuously changed in proportion to the continuous change of the compensated digital signal.
After the compensated digital signal was recorded onto the recording medium in such a recording process, this compensated digital signal is reproduced from the recording medium by the reproducing apparatus. In the reproducing process of the reproducing apparatus, the inter-symbol interference is superimposed on the reproduced digital signal. However, this inter-symbol interference does not appear in the reproduced digital signal, because the inter-symbol interference is cancelled by the predicted inter-symbol interference signal that has been subtracted from the digital signal in the stage of recording.
Thus, according to the method in accordance with the present invention, the inter-symbol interference can be eliminated. Therefore, the digital signal recorded on the recording medium can be accurately reproduced by the reproducing apparatus.
The above-stated object can be also achieved by a recording apparatus in accordance with the present invention. This recording apparatus is an apparatus for recording digital signal representing digital data onto a recording medium by changing a position of each edge of each of a plurality of pits in accordance with the digital signal. The recording apparatus is used in a recording and reproducing system together with a reproducing apparatus for reproducing the digital signal recorded on the recording medium from the recording medium. The recording apparatus includes: a receiving device for receiving the digital signal to be recorded; a predicting device for generating a predicted inter-symbol interference signal by predicting inter-symbol interference contained in a reproduced signal from the recording medium when a reproducing process is carried out with respect to the recording medium by the reproducing apparatus, on the basis of predetermined characteristics of a recording process in the recording apparatus, predetermined characteristics of the reproducing process, and the received digital signal; a compensating device for generating a compensated digital signal by subtracting the predicted inter-symbol interference signal from the received digital signal; and a recording device for recording the compensated digital signal onto the recording medium by continuously changing the position of each edge of each of the plurality of pits in proportion to the compensated digital signal.
According to this apparatus, the inter-symbol interference can be eliminated when the digital signal is reproduced from the recording medium by the reproducing apparatus. Therefore, the digital signal can be accurately reproduced.
The nature, utility, and further feature of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings briefly described below.